Improvement in sun-dials



H1l C. PEARSONS.

sun Dial. L No. 78,392. Patented May 26, 1868.

UNITED lSTATEs PATENT OEEIcE.

HARRISON C. PEARSONS, OF FERRYSBURG, MICHIGAN. u

IMPROVEMENT IN SUN-DIALS.

Specification forming part of Letters Patent No. 78,392, dated May 26, 1868.

To all 'whom it may concern:

Be it known that I, HARRISON C. PEAR- soNs, of Ferrysburg, in the county of Ottawa and State of Michigan, have invented a new and useful Improvement in a Universal Sun- Dial; and I do declare that the following is a true and accurate description thereof, referenc being had to the accompanying drawings, and to the letters of reference marked thereon, and being a part of this specification.

The nature of this invention is so to construct a sun-dial that it can be used in any part of the world, which is done by means of a hinge-joint, which renders -it adjustable to any place, and is thereby made an article of commerce for all parts of the world, whereas the ordinary dials in present use are local, or good for nothing except in the particular latitude for which they are constructed.

The equatorial dial, as heretofore constructed, can show the time only during a few hours in the middle of the day, in consequence ofthe rapid increase of the tangents of the hour-angles after getting three or four hours away from the meridian7 whereas the semicylinder, as employed in this 'combined dial, shows the time for twelve hours, the full maximum of the day during the winter half of the year.

The time could be shown during the whole year on the two faces of the plane or polar dial; but during the winter half it would be seen on the lower face, and to avoid this inconvenience of position I combine the equatorial with the polar dial.

Another object attained by the combination of these dials is simplicity of construction.

In the ordinaryT horizontal dials the hourangles are found by an equation in spherical trigonometry for determining a spherical triangle, or by an equation of plane trigonometry for determining one of the plane triangles about a solid angle, or by a theorem in descriptive `geometry for projecting the elements in one plane onto another plane, oblique to the former, the data in all cases being the latitude of the place and the earths axial motion in arc per hour, thus putting its construction beyond the reach of those not well acquainted with those branches of mathematics; whereas the graduation of my combined dial depends simply on the reduction of arc to time at the rate of fifteen degrees per hour, thus brin ging its construction within the reach of any ordinary mechanic.

My dial is in position when the following conditions prevail, viz: The gnomon must be in the plane of the meridian and at right angles to the plane of the horizon, and its upper edge, casting the shadow, and which may be called the axis of the dial, must be parallel with the earths axis. This is attained by making the angle between the horizon and the axis of the dial equal to the latitude ofthe place where the dial is to be used, by means of the graduated arc of a circle attached to the gnomon.

The polar dial must have its plane at right angles to the axis of the combined dial. Itis then in a plane parallel with that ot' the equator.

The equatorial dial must have the axis of its semi-cylinder coincident with the aXis of the combined dial, and with the edge of the gnomon casting the shadow.

It will be seen that there are two centers from which the graduations of the dial are made, the thickness of the gnomon determining the horizontal distance between them.

The whole being in position, the time will be accurately shown during the winter half of the year upon the cylindrical dial, and for the summer half of the year it will be shown on the upper face of the plane or polar dial.

My dia-l may be constructed of any appropriate material.

What I claim as my invention, and desire to secure by Letters Patent, is-

The combination of the polar dial A and the equatorial dial B with the semi-cylinder O, when employed instead of a plane surface for the equatorial dial.

HARRISON C. PEARSONS. Witnesses:

HIEAM A. REED, GEO. W. COLE. 

